1. Field of the Invention
The present invention relates to a method for recording an information signal on a recording disc, and more specifically to a recording method in which an information signal including a synchronizing signal is recorded along a concentric or a spiral track formed on the recording disc.
2. Description of Background Information
A video disc is used for recording an FM modulation signal of an information signal including a synchronizing signal, such as a video signal. The recording methods for recording the video disc are classified as a constant angular velocity (CAV) method and as a constant linear velocity (CLV) method.
In the case of a disc recorded by the CAV method, that is a CAV disc, the positions of the portions of the recording tracks in which the synchronizing signal is recorded are aligned on the same radius of the disc. Therefore there is an advantage in that the crosstalk phenomenon (a disturbance of the reproduction of the recorded signal because of a synchronizing signal of an adjacent recording track) is eliminated. However, this type of disc is not suited for long recording times since the density of recording is relatively low due to the reason that sections of the recording tracks in the outer part of the disc tend to be by far longer than the length which is required to record a piece of video signal. This is caused by the necessity of securing a minimum length of the section of recording track between horizontal synchronizing signals, i.e., a piece of video signal in the inner part of the video disc.
In the case of a disc recorded by the CLV method, that is a CLV disc, on the other hand, the density of recording is relatively high because the length of the section of recording track between horizontal synchronizing signals is made constant throughout the recording tracks. However, there is a disadvantage in that crosstalk cannot be eliminated because the positions of the recording tracks in which the horizontal synchronizing signals are recorded are not aligned on the same radius of the disc. Therefore, a signal detected by a pickup means has a beat component corresponding to the difference of the frequency of the video signal and the frequency of a horizontal synchronizing signal. And consequently, a picture reproduced on a display device is deteriorated by the beat component. Thus, the CLV disc has the disadvantage of crosstalk in spite of the advantage of the high recording density.
In order to eliminate the above-mentioned drawbacks of the CAV disc and the CLV disc, an improved recording method has been developed by the present applicant in which there is provided on a single disc, a first portion of recording tracks for recording signals by rotating a disc at a constant angular velocity, and a second portion of recording tracks for recording signals while varying the angular velocity. The basic technique is disclosed in U.S. patent application Ser. No. 446,657, filed Dec. 3, 1982.